The present invention relates generally to miniature instrumentation for chemical analysis and chemical sensing and, more specifically, to electrically controlled manipulations of fluids and capillaries in micromachine channels. These manipulations can be used in a variety of applications, including the electrically controlled manipulation of fluid for capillary electrophoresis, liquid chromatography, and flow injection analysis.
Capillary electrophoresis has become a popular technique for separating charged molecular species in solution. The technique is performed in small capillary tubes to reduce band broadening effects due to thermal convection and hence improve resolving power.
The small tubes imply that minute volumes of materials, on the order of picoliters, must be handled to inject the sample into the separation capillary tube.
Current techniques for injection include electromigration and siphoning of sample from a container into a continuous separation tube. Both of these techniques suffer from relatively poor reproducibility, and electromigration additionally suffers from electrophoretic mobility-based bias. For both sampling techniques the input end of the analysis capillary tube must be transferred from a buffer reservoir to a reservoir holding the sample. Thus, a mechanical manipulation is involved. For the siphoning injection, the sample reservoir is raised above the buffer reservoir holding the exit end of the capillary for a fixed length of time.
An electromigration injection is effected by applying an appropriately polarized electric potential across the capillary tube for a given duration while the entrance end of the capillary is in the sample reservoir. This can lead to sampling bias because a disproportionately larger quantity of the species with higher electrophoretic mobilities migrate into the tube. The capillary is removed from the sample reservoir and replaced into the entrance buffer reservoir after the injection duration for both techniques.
U.S. Pat. No. 4,908,112 to Pace describes a micro-machined structure that includes a channel for the separation and a separate channel that meets the separation channel in a T-intersection and contains electrodes to produce electroosmotic flow for injection of sample into the separation channel.
U.S. Pat. No. 5,141,621 to Zare et al. discloses a capillary electrophoresis method and apparatus which applies a potential at two buffer reservoirs located at opposite ends of a capillary column. Samples are introduced without the need to disengage the electyric field, due to the fact that the injector is grounded.
U.S. Pat. No. 5,110,431 to Moring describes a crossing flow pattern using conventional capillary tubing with minimal resolution loss for the purpose of post column introduction of reactive substances to aid in detection.
U.S. Pat. No. 5,092,973 to Zare et al. describes a capillary with rectangular geometry, which certain specified advantages in a capillary electrophoresis technique.
U.S. Pat. No. 5,073,239 to Hjerten discloses the use of two capillaries to deliver sample by electroendosmotic flow into a closed container whose major exit is through the separating column.
A continuing need exists for methods and apparatuses which lead to improved electrophoretic resolution and improved injection stability.
An object of the present invention is to provide a miniaturized injection method and apparatus in which it is not required to perform any mechanical manipulations with the capillary tube.
Another object of the present invention is to provide a miniaturized injection method and apparatus which utilizes electroosmottic pumping similar to electromigration techniques, but without the advent of sampling bias.
Yet another object of the present invention is to provide a miniaturized injection method and apparatus capable of achieving improvements in reproducibility of injections.
Still another object of the present invention is to provide a miniaturized injection method and apparatus which uses electrostatic forces to spatially shape the injection plug, making it small in spatial extent and stable with time.
Another object of the invention is to provide a reagent mixing apparatus and method for electroosmotically driven devices which allow virtually any wet chemical experiment now performed at the bench, in test tubes and beakers, to be conducted on a chip under electronic control.
These and other objects of the invention are met by providing a method of controlling fluid flow in an interconncected channel structure having at least three ports, which includes actively controlling the electric potential at the at least three ports to create diffferences in potential sufficient to cause fluid to move through the interconnected channel structure in a controlled manner. The aforementioned objects are further met by providing an apparatus for effecting the method.
In another aspect of the invention, an injection apparatus is provided for microchip liquid chromatography and other situations, which includes a body having a first channel extending between an analyte reservoir and an analyte waste reservoir and a second channel extending between a first buffer reservoir and a buffer waste reservoir, the first and second channels crossing to form a first fluid communicating intersection, and means for moving analyte, in sequence, and at first, through the first channel into the intersection, and then from the intersection into the second channel.
Other objects, advantages and salient features of the invention will become apparent from the following detailed description, which taken in conjunction with the annexed drawings, discloses preferred embodiments of the invention.